The present invention relates to a driver circuit of a liquid crystal display device (hereinafter referred to as an LCD) and, more specifically, to a driver circuit of a matrix type LCD having a data latch circuit for latching digital input data in response to sampling pulses that are generated based on horizontal scanning.
Under the current technologies, in producing what is called a driver circuit integration type LCD in which a driver circuit system is formed by using polysilicon TFTs (thin-film transistors) so as to be integral with a pixel (liquid crystal) system, a high power supply voltage and a high clock pulse voltage are necessarily required because the characteristics of a polysilicon TFT are inferior to those of a single crystal silicon transistor. Typically, a power supply voltage VDD is set higher than 13 V.
At present, low power consumption type mobile computers are being developed and commercialized actively. For an LCD to be used for this purpose, it needs to satisfy a condition of low power consumption. However, as described above, an LCD consumes large power when VDD is set higher than 13 V, for example. Further, since an input timing system needs a high voltage, it is necessary to effect voltage increase from an input voltage of the TTL level or the 2.7-V system to a voltage of the 13-V system inside or outside the LCD panel. Therefore, in the aspect of the system configuration, the use of a booster circuit causes increase in circuit scale and power consumption but also undesired emission.
On the other hand, where the common inversion driving method is used which is a commonly known liquid crystal driving method, a dynamic range of about 5 V is sufficient for a driver circuit system. The common inversion driving method is a driving method which can approximately halve the effective voltage of an external input video signal by varying the opposed electrode voltage with a phase opposite to that of the input signal. Although the common inversion driving method is a promising method for reducing the power consumption of mobile LCDs, the driver circuit system is a major factor of obstructing development of low power consumption LCDs because of insufficient device performance.